Prior art in the area of throttle position sensor error handling generally employs some form of substitution of a calculated value for throttle position if an error is detected in the signal from the throttle position sensor. Some systems also will cease substitution of a calculated value and return to using the actual throttle position signal when the malfunction is no longer detected.
The methods of substitution are varied in form. A simple method is using a value which will allow the vehicle to function in a reduced capability mode providing limp-home operation. A second method makes use of two or three values for the throttle position which are selected according to other engine parameters. This offers a more improved limp-home capability by providing a wider range of throttle position values under which the engine can operate. A third method of substitution uses a map to provide throttle position as a function of manifold pressure and/or some other engine operation condition parameter. The goal of this method is to make the presence of an error in the throttle position sensor transparent to the driver.
Prior art also recovers from the disappearance of a throttle position sensor error in varying ways. Some control systems do not attempt to return to the actual throttle position value and continue using a selected method of substitution. Other control systems return to the actual signal returned by the sensor once it is found to be operating properly. Re-establishing the use of the actual throttle position sensor may be accomplished by ramping from the substituted value to the actual value gradually each time that the controller must produce a throttle position value. The main drawback of these methods of recovery is that because gear selection is based on throttle position, unexpected and unwarranted shifting may occur. Such shifts are an annoyance to the driver especially when occurring while in a constant speed mode.